Bicycle rear wheel sprocket arrangements are generally known as bicycle components. They are used, for example, in the tourer bicycles, racing bicycles and in the mountain bike sectors at locations where derailleur mechanism gears are provided in bicycles in order to bring about different transmission ratios from the tread crank to the rear wheel. In this instance, the number of sprockets on the rear wheel has increased over time in order to graduate transmission ratios more and more finely. This fineness of the graduation was even further supported by an increasing number of chain rings on the tread crank.
Recently, there has been perceived a development tendency which again reduces the number of chain rings which are directly connected to the tread crank. This may lead to singular derailleur mechanisms in which only a single chain ring is provided on the tread crank. With the reduction in the number of chain rings, the number of sprockets in the rear wheel sprocket arrangement and the tooth number graduation thereof assumes increasing importance for producing desired transmission ratios.
Reference may be made to the publication U.S. Pat. No. 3,748,916 A of Morse by way of example of a bicycle rear wheel sprocket arrangement of the generic type for a single derailleur mechanism. This publication discloses a bicycle rear wheel sprocket arrangement with a total of 5 sprockets, of which the smallest may have 9 and the largest may have 45 teeth. Consequently, that sprocket arrangement has a gear range quotient of 45:9=5. Consequently, the gear range quotient is a measurement for the bandwidth of transmission ratios which can be produced with a sprocket arrangement. The greater the value of the gear range quotient, the greater the bandwidth of transmission ratios which can be produced.
The technically most advanced prior art in the field of single derailleur mechanisms may currently be a system which is marketed by SRAM under the name “XX1”. This system with a rear wheel sprocket arrangement comprising 11 sprockets has a gear range quotient of 4.2.
Reference is further made as additional prior art to EP 2 022 712 A of Campagnolo, which discloses a 12 sprocket arrangement whose smallest sprocket has 11 teeth and whose largest sprocket has 27 teeth. The gear range quotient of that sprocket arrangement is, at 2.45, slightly less than half as large as that of the sprocket arrangement of the previously discussed US patent.
Reference may be made to U.S. Pat. No. 5,954,604 A as another extreme example of a multiple sprocket arrangement which sets out a sprocket arrangement having 14 sprockets. FIG. 13 of this publication shows an embodiment in which the smallest sprocket of the sprocket arrangement has 11 teeth and the largest sprocket has 39 teeth. Therefore, the gear range quotient of that known sprocket arrangement is 3.54.
In a more comprehensible manner, the number of sprockets in the sprocket arrangement gives a measurement of the fineness of the graduation of the transmission ratios which can be achieved with a rear wheel sprocket arrangement. The higher the number of sprockets, the finer the graduation of the adjustable transmission ratios can be.
However, there is only limited structural space available for the arrangement of the rear wheel sprocket arrangement on a rear wheel hub. Because of this limited structural space the number of sprockets in the sprocket arrangement cannot be freely increased. Therefore, the packing density quotient mentioned in the introduction directly gives a measurement of how effectively the structural space present on the rear wheel hub is used for the arrangement of sprockets. Indirectly, the packing density quotient is also a measurement concerning the fineness of the graduation of the achievable transmission ratios because it contains in the numerator information relating to the number of sprockets in the rear wheel sprocket arrangement. Again, the following applies: the higher the packing density quotient, the more effective is the use of structural space for the arrangement of sprockets. Similar to the gear range quotient, the packing density quotient is a dimensionless numerical value, for the establishment of which only the numerical value of the spacing measured in millimeters (“mm”) between the axially outermost sprockets should be used.
The 5 sprocket arrangement known from U.S. Pat. No. 3,748,916 A takes up, for example, an axial structural space of approximately 26 mm. Consequently, the packing density quotient purely as a numerical value variable of this sprocket arrangement is 0.192.
In comparison, EP 2 022 712 A for the 12 sprocket arrangement, the implementation of which is not demonstrated in the publication, however, sets out an axial structural space requirement of 40.5 mm. This results in a packing density quotient of 0.296.
The above-mentioned single derailleur system “XX1” of the same Applicant has, with 11 sprockets in a structural space of 38.4 mm, a packing density quotient of 0.286.
Finally, reference may be made as an additional comparison to the above-mentioned U.S. Pat. No. 5,954,604 A in which 14 sprockets of a sprocket arrangement are received with an axial spacing of the outermost sprockets which axially measures approximately 50 mm, which results in a packing density quotient of approximately 0.28.
As evidenced herein, modern rear wheel sprocket arrangements have a packing density quotient of slightly below 0.3. This sets out the current state of axial structural space use on rear wheel hubs.